Background

Brucellosis is a serious zoonotic infection disease that is endemic worldwide. It causes serious economic loss and is a threat to public health, contributing to a heavy burden of disease globally [1, 2]. Its prevalence has been gradually declining in traditionally high prevalence areas, such as the Mediterranean Basin, France, and Latin America; however, epidemics and outbreaks occur in several countries, particularly in the countries of the Near East, and Central Asia, Furthermore, the disease is still in varying trends, both in European countries and in the USA [3]. In 2013–2017, the annual incidence ranged from approximately 0.0301–0.2357/100.000 in Anhui province and has been increasing yearly in recent years [4]. The common clinical manifestations of brucellosis include fever, fatigue, and joint and muscle pain, leading to multiple system damage [5] and showing a wide range of clinical polymorphisms that mimic many diseases. Epidemiology is often not easy to trace owing to the limited range of movement of children, particularly in those originating from non-pastoral areas, resulting in a high rate of misdiagnosis, treatment delay, and increased incidence of chronic illness and complications. Herein, we summarize the epidemiological and clinical characteristics of five children diagnosed with brucellosis who were admitted to our hospital and provide a review of the literature to enhance the diagnostic rate of brucellosis and ensure timely treatment.

Methods

This retrospective and descriptive study was conducted on five children with brucellosis admitted to our hospital between January 1, 2021 and December 30, 2022. Microsoft Excel 2019 was used to collect the data from the hospital information system, including demographic information, clinical manifestations, laboratory examination results (complete blood count, hemoglobin level, platelet count, erythrocyte sedimentation rate, C-reactive protein, procalcitonin, ferritin, aminotransferase, blood and bone marrow cultures, bone marrow cytology), and cervical lymph node B-ultrasound, abdominal B-ultrasound, joint magnetic resonance imaging (MRI).

Brucellosis was diagnosed based on China’s national guideline for the “Diagnosis for Brucellosis [6].” First, clinical manifestations, such as fever, sweating, fatigue, and joint pain, were assessed. Second, the presence of Brucella spp. in blood or bone marrow culture was determined. The Bac-Tac blood-culture system(BACT/ALERT® 3D, BioMérieux) was used for determining the results of the blood or bone marrow culture, and the VITEK2 compact system(BioMérieux, China) was used for bacteria identification after Gram staining.

Results

General information and epidemiology

All five patients were from non-pastoral areas of the Anhui province, with ages ranging from 2 to 12 years, with three cases living in rural areas. Disease onset was in spring and summer. Four of the five patients were male. Three children had a history of sheep contact, one ate sheep meat, and one had no history of suspicious contact with animals or consumption of animal and dairy products (Table 1).

Clinical characteristics

The initial symptom was medium- to high-grade fever, the pattern of which was not fixed. The course of the disease was mostly accompanied by night sweats, fatigue, and poor appetite. Three cases reported joint pain (Case 3: hip, knee, and ankle; Case 4: hip and knee; Case 5: shoulder, hip, and knee). Physical examination showed enlargement of the cervical lymph nodes and liver/spleen in all children (Table 1).

Table 1 General information and clinical characteristics of 5 children with brucellosis
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Auxiliary examination

The white blood cell count was normally or mildly elevated, with lymphocytes as the predominant cell population. The serum levels of C-reactive protein and procalcitonin were normal or mildly raised (Table 2). Four cases had anemia, one had thrombocytopenia, four had elevated ferritin levels (> 150 ng/mL), and four had liver function abnormalities. Blood cultures were positive in five cases, including one with a positive bone marrow culture. Imaging findings detected hepatomegaly in three cases, splenomegaly in five, and enlarged cervical lymph nodes in five (> 1.5 cm). MRI revealed joint cavity effusion in two patients who had transient joint symptoms, one patient with recurrent joint pain developed cortex of bone damage at follow-up. (Fig. 1).

Table 2 Laboratory examination of 5 children with brucellosis
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Fig. 1
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MRI scan images. A/B/C: High T2 signals in the sacroiliac joints(the dates were June 2021 / July 2022 / January 2023, respectively) of case 3. D: Joint cavity effusion in hip joint of case 5. E: Joint cavity effusion in the knee joint of case 5

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Treatment and follow-up

For 6 weeks, oral rifampicin combined with doxycycline was prescribed in children aged more than 8 years, while oral rifampicin combined with cotrimoxazole was prescribed in those aged less than 8 years. This treatment course achieved satisfactory results. No severe adverse drug reactions were reported. One child (Case 5) had persistent neutropenia, which gradually returned to normal 2 weeks after treatment completion. At 1-year follow-up, four children were completely cured, but one child (Case 3) had multiple episodes of joint pain, which was relieved by supportive treatment with antibacterial drugs for 4 months. Later, intermittent joint pain was reported, and this was treated regularly with non-steroidal anti-inflammatory drugs and biologics in the rheumatology department.

Discussion

Brucellosis is the most common zoonotic infectious disease worldwide caused by infection with the bacterium Brucella, It is transmitted to humans through host animals such as sheep, cattle, camels, and even amphibians, thus affecting human health and the livestock industry [7, 8]. In China, human brucellosis occurs mainly in the northern region where livestock farming is well-developed, including Inner Mongolia, Ningxia, and Liaoning [9, 10]. With the development of animal husbandry, transportation, and tourism, the incidence of the disease increased significantly in the south coast and southwest region [11, 12]. The epidemic gradually spread from pastoral and semi-pastoral areas to urban and rural areas; however, the northern region remains the center of the epidemic.

Brucella is mainly transmitted through contact with infected animals, including goats, cattle, and pigs, or animal excrement and consumption of unpasteurized animal and dairy products [13, 14]. Occasionally, inhaling infectious aerosols carrying Brucella may cause the disease, which is a primary cause of laboratory-acquired infections [15]. An intrauterine infection route and person-to-person transmission have also been reported [16, 17]. There has been a shift in the transmission pattern of brucellosis from direct contact to food-borne. In children, it is more often transmitted through the digestive tract [18]; however, the epidemiologic history cannot be traced clearly in most patients, making diagnosis extremely difficult [19]. In this study, three of the five children lived in rural areas and had a history of animal exposure, i.e., playing with sheep. However, we did not screen the animals that came in contact with the children for brucellosis; thus, the infection sources could not be completely identified. We suggest that brucellosis screening of animals that came into contact with the patient is necessary. By contrast, the other two patients lived in the city, with good sanitary and hygienic conditions, and had no history of animal contact before the onset of the disease. We suspected that they may have been infected through the gastrointestinal route. No guardian of the children infected with Brucellosis was identified. Moreover, most patients in this study were boys. We attributed this to the fact that boys have a wider range of activities and are, therefore, more likely to be exposed to animals. A detailed epidemiologic history, including the surrounding living conditions and eating habits, should be obtained when brucellosis is suspected; however, this should not be limited to a history of animal contact but also include the meat and dairy products consumed that may have been contaminated by the bacteria. The diagnosis of brucellosis should not be excluded in the absence of a definite history of exposure, which may result in misdiagnosis.

Brucellosis is a multisystem disease, with nonspecific clinical symptoms including fever, malaise, night sweats, and myalgia arthralgia [20]. Fever is the most frequent symptom; however, owing to the extensive abuse of antimicrobial drugs, the typical undulant fever is uncommonly observed. Two misdiagnosed children were treated with multiple antibiotics, including cefuroxime, cefazoxime, amoxicillin clavulanate potassium, and azithromycin, before a definitive diagnosis was made. However, owing to the specific pathogenesis of Brucella, once the pathogen enters the macrophage system, the clinical symptoms may be relieved, presenting only as an intermittent pattern of fever, thereby creating the clinical illusion that the treatment is effective. Arthritic symptoms are less common in children than in adults and tend to involve peripheral joints, especially the knee and hip joints [21]. In this study, all five patients had a fever, accompanied by different extents of malaise and night sweats. Three children had joint pain and dyskinesia, with joint effusion shown by magnetic resonance imaging. All cases had lymph node and liver/spleen enlargement, which are more common in children than in adults since the former have underdeveloped immune systems that are more likely to be affected [22]. Recurrent fever is the most common cause of clinical visits among children, and the other signs and symptoms are not specific, especially in patients originating from non-endemic areas. These cases can be easily overlooked by clinicians, leading to misdiagnosis. Therefore, pediatricians should consider brucellosis among children with fever of unknown origin.

Patients with brucellosis can have abnormal laboratory test results, with anemia, leukopenia, thrombocytopenia, elevated liver enzymes, and elevated CRP as the most commonly reported in acute and subacute cases [23, 24]. However, because laboratory test results are usually variable and nonspecific, they cannot help clinicians in making a diagnosis, especially in the absence of epidemiologic data. Culture isolation of Brucella abortus is the gold standard for the diagnosis of brucellosis [25]. Blood is the most commonly used material for bacterial culture. In this study, all patients had a positive blood culture for Brucella melitensis, thus confirming the diagnosis; however, two patients were misdiagnosed at the first admission due to negative blood culture results and misidentification as Micrococcus garcinia, respectively. As the infection proceeds, isolation of pathogenic bacteria from blood specimens becomes increasingly difficult, as the pathogen enters the macrophage system [26]; therefore, early specimen collection is essential. Positive rates may be increased by culture of macrophage-rich tissues, such as bone marrow, liver, and lymph nodes, especially in patients living in areas with high antibiotic use and those with chronic cases [27]. Acquisition of these specimens can be invasive and painful. Furthermore, microbiologists should have sufficient experience to avoid misidentification, as Brucella is a small, short Gram-negative bacterium [28, 29]. Many factors, such as time of culture, initial infection, and recurrence, affect the rate of positivity for Brucella cultures. Because of such limitations of Brucella blood culture, complete reliance on culture results may increase the likelihood of misdiagnosis.

Compared with traditional detection methods, multiplex nucleic acid amplification technology is a more convenient and effective diagnosis technique for brucellosis [30, 31]. Serologic tests are the most widely used due to their simplicity, rapidity, and inexpensiveness in developing countries [32,33,34]. Frequently used serologic methods for brucellosis include the Rose Bengal test (RBT), standardized tube agglutination (SAT), and enzyme-linked immunosorbent assay (ELISA)-IgM/G. SAT can detect positive cases as early as the second week after the onset of illness and has a high level of specificity [35, 36]. Compared to the SAT, the ELISA-IgM/G has better diagnostic specificity and sensitivity, especially in chronic cases [37]. The RBT is a simple and rapid screening method usually used in epidemiological studies [38]. However, serologic tests are influenced by the patient’s immune response and cannot, therefore, provide direct evidence of microbial infection. Hence, combined serologic tests are recommended to avoid overdiagnosis and unnecessary antimicrobial therapy and should be interpreted according to clinical situations. In this study, serologic examination was performed in all five children after diagnosis, and all showed positive findings. Because of limited experience, we had not considered the possibility of brucellosis initially and did not send for serological tests, resulting in misdiagnosis in two children. Because it is economical and yields rapid results, serological testing should be performed in children with fever of unknown origin who are suspected of brucellosis. This recommendation may improve diagnostic accuracy by combining serologic testing.

Most brucellosis cases have a benign course, and timely and standardized treatment can achieve satisfactory results. However, Brucella may escape attack by the host’s innate and adaptive immune response and remain in host cells for long periods, making the treatment difficult and not easily removable [39, 40]. When therapy is delayed, the disease can become chronic or lead to serious complications, among which osteoarticular involvement is the most common [19]. All five cases in this study were treated according to the recommendations of the World Health Organization [41], achieving satisfactory therapeutic outcomes. One patient who was misdiagnosed reported recurrent joint pains in the knee, ankle, and hip joints, which caused serious disruption to his life and studies. Thus, timely diagnosis and standardized treatment are of great significance to improve disease prognosis.

Conclusions

Because the epidemiology of brucellosis in children is difficult to trace in non-pastoral areas and cases have diverse and non-specific clinical symptoms, it can be easily misdiagnosed. Thus, in treating children with fever of unknown origin, pediatricians should review their epidemiological history in detail and perform combined serologic examinations to improve the diagnosis rate to reduce the complications and burden of disease. Timely and accurate diagnosis and treatment are crucial to improve prognosis.